Terence I think you are correct. That is a huge problem, and probably always will be. Across the tango styles there are basic elements of movement, and an understood standard of correctness of movement. (Incidentally, this is how I was taught Salsa as well.) This is why my philosophy has been to focus on the very basic elements and build from there.

I can use the OPs question as an example. In this case, OP was asking two questions without knowing it. Question 1: "How do I properly execute an ocho?" and Question 2: "How do I properly embellish an ocho?" I dont want to "bash" OPs instructor, but it would appear that OPs instructor could not make the distinction between an element of movement and an embellishment of that movement. But, to take OPs question further, regardless of style, proper ocho execution would be to pull from the inner thighs, dance on inside edges of feet, maintain weight on supporting foot while rotating... When we come to matters of embellishment, or even discuss the degree of rotation, we begin to get into areas of differences that define style. Unfortunately, this is where you start finding instructors who will tell you X is correct and Y is wrong, when they are addressing issues of style, and not basic movement. Why this is done I do not really know. It could be argued they simply do not know the difference, or perhaps they are trying to market their own special style of tango... The student suffers either way.